This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-207400, filed Jul. 7, 2000, the entire content of which is incorporated herein by reference.
The present invention relates to a component rolling tool for forming a dynamic pressure groove on an inner peripheral surface of a bearing hole in a dynamic pressure bearing by moving a plurality of component rolling balls in pressure contact with the inner peripheral surface, and a component rolling method using the same.
Conventionally, a component rolling tool and method of the dynamic pressure groove using the component rolling ball have been known, for example, in Japanese Patent Application KOKAI Publication No. 11-77210.
The component rolling tool disclosed in Japanese Patent Application KOKAI Publication No. 11-77210 has a sleeve, component rolling balls, a moving roller and an urging member.
The sleeve has one end and the other end, and has a longitudinal center axis. The sleeve is formed in a hollow cylindrical shape having a center hole extending along the longitudinal center axis. The center hole is open in a side of one end of the sleeve. The sleeve has a plurality of guide holes. The component rolling ball is mounted in each of the guide holes.
The moving roller is arranged in the center hole of the sleeve so as to freely rotate about the longitudinal center axis and freely reciprocate along the longitudinal center axis, in such a manner as to be coaxial with the center hole.
The component rolling ball is pressed by the moving roller in the center hole and is protruded outward from the guide hole at a predetermined amount.
The urging member has one end and the other end and is arranged in the center hole. The urging member is provided such that one end thereof is connected to the other end of the moving roller and the other end thereof is connected to the other end in the center hole. The urging member urges the moving roller toward the other end side along the longitudinal center axis.
Then, in accordance with the component rolling method of the dynamic pressure groove using the component rolling tool, the sleeve is driven so that the sleeve is inserted to the bearing hole from an external portion of the bearing hole. Next, in a state that a plurality of component rolling balls are in pressure contact with the inner peripheral surface of the bearing hole, the sleeve is moved in a direction of the axis while being rotated about the axis. Together with this movement, the component rolling tool applies a forming of the dynamic pressure groove onto the inner peripheral surface. The component rolling method uses the component rolling tool to execute the component rolling process in the manner mentioned above. In this case, the initial position means a position at which the moving roller is arranged before starting the component rolling process.
In the conventional component rolling tool mentioned above, the component rolling ball is exposed to an external force to be rotated due to a contact with respect to the inner peripheral surface of the bearing hole at a time of forming the groove. In this case, in the component rolling tool mentioned above, the moving roller is to freely rotate about the longitudinal center axis of the component rolling tool in the center hole of the sleeve, and is to freely move to one end side along the axis. Accordingly, the component rolling ball can rotates while rotating the moving roller being in contact with the component rolling ball itself and moving the moving roller to the side of one end, in the case of being exposed to the external force. Accordingly, a load generated between the component rolling ball and the inner peripheral surface of the bearing hole does not become equal to or more than a force necessary for forming the dynamic pressure groove, so that no burr and no peeling are generated on the formed surface of the dynamic pressure groove.
The moving roller is kept being gradually moved to the side of one end due to the rotation of the component rolling ball in correspondence to the movement of the sleeve. The moving roller is forcibly urged in a direction along the axis in an opposite side to the forward moving direction of the sleeve by the urging member provided in the center hole of the sleeve in the manner mentioned above when the component rolling ball becomes in a state that the component rolling ball is not in pressure contact with the inner peripheral surface of the bearing hole in the dynamic pressure bearing, thereby being returned to the initial position.
In accordance with the component rolling tool and method of the dynamic pressure groove as mentioned above, it is possible to stabilize a quality of the formed surface of the dynamic pressure groove and it is possible to continuously form the dynamic pressure groove.
The component rolling method of the dynamic pressure groove is generally executed in accordance with the following procedure.
1. The component rolling tool is inserted to the bearing hole of the dynamic pressure bearing from the other end of the bearing hole, is forward moved along the axis, plastically works the inner peripheral surface of the bearing hole by the component rolling ball, and forms the dynamic pressure groove on the inner peripheral surface.
2. The component rolling ball temporarily moves out of the bearing hole from one end of the bearing hole.
3. The component rolling tool is rearward moved along the same path as that at a time of plastically working in the process mentioned in the item 1 (the component rolling ball moves along the same path inversely).
In accordance with this procedure, in the conventional embodiment described in Japanese Patent Application KOKAI Publication No. 11-77210, when the component rolling ball temporarily moves out of the bearing hole from the other end of the bearing hole in the manner mentioned above, the load due to the pressure contact of the inner peripheral surface of the bearing hole with respect to the component rolling ball is lost, so that the moving roller is returned to the initial position by the urging member in spite that it is not an intended timing. In this state, when rearward moving the component rolling tool in the manner mentioned above, the moving roller is moved to a position at which the moving roller can not move in a backward moving direction of the sleeve, so that the component rolling ball is hard to rotate.
Further, in the forming process of the dynamic pressure groove on the inner peripheral surface of the bearing hole, there is a case that the inner peripheral surface is not completely plastically deformed in correspondence to the outer shape of the component rolling ball only by the forward motion of the sleeve but a return back such as an elastically deformation is partly generated. Further, there is a case that there is generated a shift in view of a forming accuracy between the backward moving path of the component rolling balls and the forward moving path. Under these circumstances, in the case that the component rolling ball does not smoothly rotate, the component rolling ball during the forming on the backward moving path generates a great friction with respect to the inner peripheral surface of the bearing hole.
Further, in the component rolling method, in the case that a necessary number of the grooves to be formed is n times the number of the component rolling balls, there is a case that in order to reduce a forming man-hour, the component rolling ball moves on the different new path from the forward moving path at a time of backward moving so as to form the groove. At this time, in the case of using the conventional component rolling tool mentioned above, since the component rolling ball is, of course, hard to rotate during the forming process in the backward moving path, the component rolling ball generates a great friction with respect to the inner peripheral surface of the bearing hole in the dynamic pressure bearing.
As mentioned above, in the case that the moving roller does not move along the longitudinal center axis at a time of forming in the backward moving path, the load between the component rolling ball and the inner peripheral surface of the bearing hole to be rolled becomes equal to or greater than the force necessary for forming the dynamic pressure groove, a burr and a peeling are generated on the inner peripheral surface of the bearing hole in the dynamic pressure bearing, so that the quality of the formed surface of the dynamic pressure groove becomes unstable.
An object of the present invention is to provide a component rolling tool which can always rotate component rolling balls when the component rolling balls move through an inner peripheral surface of a bearing hole in a dynamic pressure bearing in spite of a simple structure, can prevent a burr and a peeling from being generated on the inner peripheral surface of the bearing hole in the dynamic pressure, can form a surface to be formed of the dynamic pressure groove at a high quality for a long time, can return a moving roller to an initial position at a desired timing without requiring a troublesome operation and can continuously form the dynamic pressure groove, and a component rolling method.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.